Plaque consists primarily of microorganisms (70%), streptococci constituting the major bacterial component. Analysis has been undertaken of the chemical composition of Streptococcus sanguis, one of the predominant groups of plaque streptococci. Analysis of the cells show the following percent composition: water-84, protein-7.1, carbohydrate- 3.0, lipid-1.4, ash-1.2, RNA-0.6 and DNA-0.2. A study of the distribution of glucosyltransferase (GT) and fructofuranosidase (FH) activity in washed cells of Strep. sanguis revealed that about 64% of GT activity was located in the cell debris and 32% in the cytosol. FH activity was found only in the cell debris. About 10% of the total GT activity remained cell bound most of it being released to the culture medium. The effectiveness of plaque fractionation procedures has been studied by incubating plaque in a medium containing H3 thymidine and C14 sucrose to label both cellular and extracellular components. Plaque was dispersed and centrifuged. The supernatant was then either directly fractionated by glycerol gradient centrifugation or following millipore filtration. A C14 peak found above the cell fraction was removed by cell filtration. It was concluded that millipore filtration removed not only cellular components but also insoluble extracellular matrix and the filtrate represents only soluble extracellular material. Other plaque fractionation techniques are being evaluated.